(1) Field of the Invention
The present invention relates to taking-up liners to be used to take up unvulcanized rubber members for tires, for instance, inner liners and sheets of coated cords.
(2) Related Art Statement
Unvulcanized rubber members are sometimes temporarily stored between a step for feeding the unvulcanized rubber members and a step for using such unvulcanized rubber members. In such cases, the unvulcanized rubber members are generally temporarily stored in a rolled fashion in the state that the unvulcanized rubber member is taken up by using a taking-up liner.
In order to take up relatively thin, flat unvulcanized ruber members, fabrics made of organic fibers of, for instance, nylon, polyester, vinylon or polypropylene have first been used as liners. However, such liners form uneven portions on the surfaces of the rubber members due to their yarn meshes during the taking-up of the liners, so that tackiness of the rubber members lowers. That is, when tackiness varies at a taking-up place, working efficiency lowers at an actual use site, and problems occur in tire products in which air enters a joined portion of a tire product due to insufficient bonding forces, and a joint portion at an inner liner cracks. Further, this necessitates the application of a cement rubber, which causes a wasteful consumption of materials. In view of the above, it is a common practice that disposable sheets made of, for instance, polyethylene, polypropylene, and polyvinyl chloride, or repeatedly usable sheets in which a sheet-like elastomer having no elasticity is bonded to a base cloth having no stretchability.
On the other hand, when an unvulcanized rubber member having different rubber thicknesses in a width-wise direction, such as a rubber sheet 20 having a ridge portion as shown in FIG. 17 or a coated cord cut sheet 23 having a squeezed rubber 22 as shown in FIG. 18, is to be taken up, it is a common practice to employ taking-up members in which non-stretchable padding cloths are bonded to opposed side surfaces of a thin soft foamed member. However, such a taking-up member develops creases on the surface thereof, which form crease traces on the unvulcanized rubber member. Furthermore, since the soft foamed member is thin, the member does not uniformly contact with the ridge-provided or curved unvulcanized member when the latter is taken up. That is, since the member is locally squeezed due to locally concentrated contact, the thickness of the rubber changes. Thus, the shrinkage factor changes in the widthwise direction during storage. Consequently, when the unvulcanized rubber member is unrolled for use, it is curved (shortened) as shown in FIG. 17, which leads to poor final products.
Under the circumstances, the present inventors applied for a patent with respect to a technique for improving the above taking-up members which can contact ridge-provided unvulcanized rubber members and prevent the thickness of rubber from changing due to squeezing of the rubber members on locally concentrated contacting (Japanese Patent application Laid-open No. 61-282,000).
However, the above-mentioned liners, currently used for the relatively thin, flat unvulcanized rubber members have the following problems.
When a film of such as nylon, polyester, polyvinyl chloride, or polypropylene is used for taking-up liners, tackiness of the rubber members is improved. However, they have practically many problems in that they are uneconomical being a disposal type, the film is weakened or cut during unrolling for shaping due to low strength of the film to deteriorate peelability between the rubber and the liner and greatly damage workability.
The taking-up liner in which a non-stretchable elastomer is bonded to one or both of opposite surfaces of a base fabric made of organic fibers having low stretchability to mitigate the problems of the above taking-up liners has itself no stretchability. Thus, if the liner slightly deviates from its way during taking-up for use, the manner that the liner is pulled varies in the liner width direction. Consequently, a slackened portion of the liner is taken up in the form of a crease as it is, so that the creases of the liner bites the surface of the unvulcanized rubber member to produce unacceptable products having poor properties. In order to solve such a problem, a method is conceivable for making the liner more stretchable by lowering its strength. In this method, a certain effect can be expected in an initial use stage. However, as the liner continues to be used, stress of the liner is relaxed to cause flatting, which makes use impossible. Therefore, this method is actually not a satisfactory solution. Further, when such a liner is used for taking-up a rubber member having a non-uniform thickness in a widthwise direction, such as a ridge-provided rubber sheet or a coated cord cut sheet having squeezed rubber, the take-up diameter of the rubber member varies in the widthwise direction. That is, the take-up diameter of the thicker portion of the rubber member in which the rubber is thick is greater so that the liner tends to be stretched, while the thinner portion of the rubber member is slackened. Consequently, the rubber member is stretched in the width direction and becomes unbalanced to form creases on the liner. Further, since the thinner portion of the rubber member is not closely adhered with the liner, there is a problem in that tackiness of the rubber member lowers due to the occurrence of blooming.
Next, the taking-up liner conventionally used for taking-up unvulcanized rubber members having a non-uniform thickness in the widthwise direction has the following problems.
In the case of the conventional taking-up liners, since the rubber member is squeezed by its self-weight during temporary storage after the taking-up of the rubber member, plain woven or knitted yarn meshes of the taking-up member bite the surface of the rubber member to form uneven portions thereon. Consequently, tackiness of the rubber member greatly lower. Further, since an intensity of the uneven portions formed due to the yarn meshes varies depending upon take up locations (inner, intermediate and core portions) of the taken-up members, tackiness varies within the rubber member. For this reason, since the tackiness of the rubber member is low, holding forces at a joined portion are weak, when such an unvulcanized rubber member is bonded to other members during a tire-building process. Therefore, workability in the formation of the tire is conspicuously deteriorated. Further, such liners have problems in that air enters the joined portion, that unacceptable products are formed due to poor setting accuracy of the members, and that since the holding forces between the liner and an end portion of a top tread member are weak in the case of a dual tuber (DT) side members, an outer surface precured cement is bitten at the bonded interface to develop DT cracks. Up to now, as countermeasures for solving the problems due to reduction in tackiness of the rubber member, a rubber cement is applied to the unvulcanized rubber member before taking-up, or a film of such as nylon is used as a taking-up sheet. However, such countermeasures measure all involve difficult problems to be solved. Hence, it is an actual situation that no satisfactory taking-up liners exist.